This invention relates generally to semiconductor manufacture, and specifically to an improved method and system for fabricating semiconductor components.
Semiconductor dice are used to construct various semiconductor components, such as semiconductor packages and multi chip modules. These semiconductor components typically include a substrate on which bare semiconductor dice are mounted. For example, conventional plastic semiconductor packages can include substrates in the form of metal leadframes. During a packaging process the bare dice are attached and electrically connected to the leadframes, and then encapsulated in a plastic resin.
Besides leadframes, other types of substrates are used to construct semiconductor components. For example, other types of semiconductor packages, such as xe2x80x9cBGA packagesxe2x80x9d and xe2x80x9cchip scale packagesxe2x80x9d, include substrates which can comprise a glass filled plastic, such as FR-4, or FR-5, or in some cases silicon, or ceramic. Multi chip modules and circuit boards, can also include plastic, silicon, or ceramic substrates, on which semiconductor dice, as well as other electronic components, are mounted.
During fabrication of a semiconductor component the dice are attached to the substrate. One method for attaching the dice to the substrate is by forming an adhesive layer between the dice and the substrate. For example, die attach adhesives, such as epoxy and silicone, can be used to back bond dice to substrates. Typically, the adhesive is dispensed in viscous form from a pressurized nozzle, and then cured to harden. However, for some applications it is not practical to use an adhesive because the viscous material may undesirably adhere to the surfaces of bond pads, and other electrical elements on the die or substrate, and adversely affect the electrical characteristics of the component. Also for some applications, it may not be possible to uniformly form the adhesive layer with a required planarity and geometrical configuration.
Another technique for attaching dice to lead frame substrates employs adhesive tape. For example, during fabrication of a lead-on-chip semiconductor package, semiconductor dice are attached to a metal leadframe using double sided adhesive decals. With a typical lead-on-chip fabrication process the decals are punched with a required peripheral configuration from a length of tape. Portions of the tape that do not become part of the decal are then discarded.
While adhesive tape has been used successfully in the manufacture of plastic semiconductor packages constructed with metal lead frames, it has typically not been used in the volume manufacture of other types of semiconductor components. The present invention is directed to a method and system for fabricating various types of semiconductor components using adhesive tape to attach one or more semiconductor dice to a substrate. In addition, the present invention makes decals without wasted tape, and with accurate alignment of the decal, the substrate, and the die to one another.
In accordance with the present invention, an improved method and system for fabricating semiconductor components, such as packages, multi chip modules, and printed circuit boards, are provided.
In a first embodiment the method is used to fabricate a BGA package. The BGA package includes a substrate, a semiconductor die attached to the substrate, and one or more adhesive decals attaching the die to the substrate. In this embodiment the substrate comprises an organic polymer such as bismaleimide-triazine, epoxy or polyimide, reinforced with glass fibers. The substrate is provided as a strip of material, on which multiple BGA packages are formed, and then singulated by cutting or shearing.
The method uses one or more continuous ribbons of tape which are cut into decals, and then applied to required areas of the substrate. The tape can comprise a double-sided, multi-layered adhesive tape, such as polyimide film coated on both sides with an adhesive, or alternately a single layer of adhesive material configured as tape. The decals are cut and applied to the substrate by indexing lengths of the tape into guide openings, aligning the substrate to the openings, and then moving cutters through the guide openings to cut and place the decals on the substrate. A finished dimension (e.g., width) of each decal is the same as a width of the tape. Another finished dimension (e.g., length) of each decal is controlled by cutting an indexed length of the tape. Using this method there is no wasted tape. In addition, there are only two cut edges per decal, and only one cut is required for each index of the tape and substrate.
A system for performing the method of the invention includes the substrate, the die, and a tape cutting apparatus configured to cut, and apply, the decals to the substrate. The system also includes a substrate handling apparatus configured to align the substrate during cutting and applying of the decals.
The tape cutting apparatus includes: a support frame for rotatably mounting one or more reels of adhesive tape of a desired width; a tape guide for guiding continuous ribbons of tape from the reels into guide openings for cutting; a pair of feed rollers for continuously feeding and indexing the ribbons of tape into the guide openings; and a cutter assembly adapted to move through the guide openings to cut the decals from the ribbons of tape held in the guide openings, and to apply the decals in a desired pattern to a die mounting area of the substrate.
The substrate is positioned proximate to the guide openings of the cutter assembly by the substrate handling apparatus. The substrate handling apparatus also indexes the substrate to align selected die mounting areas on the substrate to the cutter assembly for application of the cut decals.
In a second embodiment the method is used to fabricate a chip scale package comprising a substrate, a semiconductor die attached to the substrate, and one or more cut decals attaching the die to the substrate. In this embodiment the substrate is provided as a silicon, ceramic or plastic panel on which multiple chip scale packages are formed, and then singulated. In a third embodiment the method is used to fabricate a multi chip module, or a printed circuit board, comprising a substrate on which multiple semiconductor dice are attached using cut decals.